1. Field of the Invention
The present invention pertains to the art of refrigerators and, more specifically, to tube and fin-type heat exchangers used in domestic refrigerators.
2. Description of the Related Art
Refrigerators typically include one or more enclosures or chambers for storing food or other articles to be cooled or frozen. The refrigerator housing about these enclosures includes two intersecting fluid circuits: a refrigerant circuit and a cooling air circuit. The refrigerant circuit generally includes a compressor, a condenser and an evaporator with tubing between these elements to permit the flow of the refrigerating fluid. The condenser essentially exchanges heat from the refrigerator interior to the outside air. The cooling air circuit typically includes passageways for air to travel between the enclosures, the evaporator and an impeller, such as a fan, for causing air to flow within the air circuit. These two circuits intersect at the evaporator, which enables the transfer of heat from the cooling air to the refrigerating fluid.
Evaporators for refrigerators typically include a tube and fin-type arrangement wherein a serpentine tube containing the refrigerating fluid passes through the evaporator, with air paths over the serpentine tube defined by the longitudinal length of these fins. One example of such a tube and fin-type evaporator is shown in U.S. Pat. No. 3,745,786, issued Jul. 17, 1978.
It has been found to be desirable to increase the efficiency of such tube and fin-type evaporators and to decrease the size of the evaporator. An evaporator can be made more compact by, for example, increasing the density of the fins and/or by increasing the inlet flow velocity of the cooling air. However, if fin density is increased, the normal frost build-up on the fins can clog and close the flow passages for cooling air. With such an arrangement, more frequent defrosting is required, which significantly increasing energy consumption of the appliance. Similarly, increasing the flow velocity of the cooling air into the evaporator, such as by increasing the fan speed, results in more energy consumption and increases the overall noise level of the appliance.
Other previous heat transfer enhancement methods have been found to be disadvantageous when applied to refrigerators. For example, louvered or lanced fins are considered less effective than needed because of the relatively low flow velocities of cooling air in refrigerators and the frost build-up on the louvers. Additionally, evaporators having trapezoidally shaped fins, such as the evaporator shown in U.S. Pat. No. 5,157,941 issued Oct. 27, 1992, have been found difficult to manufacture.
In a manner directly analogous to evaporators, condensers in refrigerators also function to perform heat exchange operations. With respect to refrigerator condenser heat exchangers, efforts to improve heat transfer include extending secondary heat transfer surfaces as set forth in U.S. Pat. Nos. 3,785,168 and 2,359,926, for example. Additionally, it is known to provide a refrigerator with a condenser having a folded condenser tube and wire fins as seen in U.S. Pat. No. 5,502,983. However, as with fin-type evaporators, a more compact design closes the flow passages and slows the flow of cooling air through the condenser.
Therefore, there exists a need for heat exchanger for a refrigerator evaporator or condenser having an improved efficiency which is simple and inexpensive to manufacture.